Topological Self-Assembly of Highly Symmetric Lanthanide Clusters: A Magnetic Study of Exchange-Coupling "Fingerprints" in Giant Gadolinium(III) Cages

Abstract

The creation of a perfect hollow nanoscopic sphere of metal centers is clearly an unrealizable synthetic challenge. It is, however, an inspirational challenge from the viewpoint of chemical architecture and also as finite molecular species may provide unique microscopic insight into the origin and onset of phenomena such as topological spin-frustration effects found in infinite 2D and 3D systems. Herein, we report a series of high-symmetry gadolinium(III) (S = 7/2) polyhedra, Gd₂₀, Gd₃₂, Gd₅₀, and Gd₆₀, to test an approach based on assembling polymetallic fragments that contain different polygons. Structural analysis reveals that the Gd₂₀ cage resembles a dodecahedron; the vertices of the Gd₃₂ polyhedron exactly reveal symmetry O_h; Gd₅₀ displays an unprecedented polyhedron in which an icosidodecahedron Gd₃₀ core is encapsulated by an outer Gd₂₀ dodecahedral shell with approximate I_h symmetry; and the Gd₆₀ shows a truncated octahedron geometry. Experimental and theoretical magnetic studies show that this series produces the expected antiferromagnetic interaction that can be modeled based on classical spins at the Gd sites. From the magnetization analyses, we can roughly correlate the derivative bands to the Gd-O-Gd angles. Such a magneto-structural correlation may be used as "fingerprints" to identify these cages.